Posted
by
kdawsonon Tuesday October 23, 2007 @02:55PM
from the getting-the-lead-out dept.

Hugh Pickens writes "Even low levels of lead can cause brain damage, increasing the likelihood of behavioral and cognitive traits such as impulsivity, aggressiveness, and low IQ that are strongly linked with criminal behavior. The NYTimes has a story on how the phasing out of leaded gasoline starting with the Clean Air Act in 1973 may have led to a 56% drop in violent crime in the US in the 1990s. An economics professor at Amherst College, Jessica Wolpaw Reyes, discovered the connection and wrote a paper comparing the reduction of lead from gasoline between states (PDF) and the reduction of violent crime. She constructed a table linking crime rates in every state to childhood lead exposure in that state 20 or 30 years earlier. If lead poisoning is a factor in the development of criminal behavior, then countries that didn't switch to unleaded fuel until the 1980s, like Britain and Australia, should soon see a dip in crime as the last lead-damaged children outgrow their most violent years."

Yet despite a 56% reduction in violent crime, we increased our prison population faster than we increased the national population and have a record level of people in jail. How does unleaded gas explain that?

Perhaps it's that mandatory sentencing laws for drug crimes and 3 strikes laws took a lot of violent offenders and potential violent offenders off the street, rather than less lead.

"Perhaps, but unless you can compare places with those legal features with places that don't and show there's a difference, you don't have a very impressive argument."

Yes, but finding a causal relationship between lowered crime and more people spending more time in prison is easier than finding it between lowered crime and lowered lead.

The economy in the 90s was better than in the 70s. Remember how bad inflation was under Carter? You can tie lower crime rates to a better economy (more people with jobs, more people with hope, less idle hands for the devil's work).

I'm not saying any one thing led to it. I'm just saying that you can tie a drop in crime in the 90s to a lot of things. There are more compelling theories than lead, IMO.

It is an undisputed fact that violent crime has been following the lead levels in teenagars. Lead levels up - crime rate up, lead levels down - crime rate down. Again, if you had RTFA you would know that the researchers themselves had pointed out that this is a correlation, and correlations by themselves do not prove causation. However, it is a very interesting idea and quite possibly true. Proof will come as more data arrive.You, however, thought it was a ridiculous idea. That is not so - I find the

The biggest danger now is probably from you water tap. There was a program on danish television that showed how Chinese factories use whatever scrap metal they can find to make taps. Lead is added to lower the melting point of the mixture, and it will go into the water. The also leak way too much Nickel (from when they are coated in crome, which is in fact nickel. The cheap models have the coating inside as well). They showed how everything from car parts to whatever scrap metal they could find was used. An

Doubtful. I'm no expert, but I would imagine that the amount of lead you'll absorb by handling a small toy covered in lead paint is going to be at least several orders of magnitude less than what you'd be inhaling from the emissions of every car, truck, and bus on the planet (and at 1970s emissions standards) every day.

A small toy with a coat of leaded paint is relatively inert in comparison, and even if you scraped every ounce of paint off of the toy and ingested it, I'd bet that your total exposure would be considerably less. Granted, the effects of massive single doses are probably going to be quite different than long-term exposure, and you'd probably die if you did ingest that much of a heavy metal in one go.

Widespread use of lead paint is a bad thing, as is the widespread use of leaded gas. Lead's been conclusively shown to be a carcinogen and something you want to avoid if you can. That said, unless you eat the stuff or are exposed to minute amounts in aerosol form for a prolonged period of time, it's probably not going to do a whole lot of damage. The people who produced/imported those toys should indeed be prosecuted to the full extent of the law, but I don't think it's cause for widespread panic yet.

A 1970 Challenger with almost 400 horsepower was about $25K in today's dollars. $25K today gets you something like a WRX or Mazdaspeed 3, which will absolutely _crush_ that car in anything but a straight line, and on period correct tires will also beat it in a straight line. C'mon, aside from missing that V8 engine noise, we're living in a golden age.

Actually, the paper makes an minor reference to lead-based paint. Their representation is that the absorption mechanism is less effective - it requires consumption of paint chips.As a previous poster represented, inhalation of exhaust is a very efficient vector. Also, there is contact with materials on which exhaust is deposited - soils and water. Like pesticides (or nuclear waste, for that matter), a widespread low-level exposure is all that is necessary if total dosage characteristics come into play.

I briefly read the study and she does take age into account. She uses crime rates (not absolute numbers) and finds a correlation between lead exposure in youth and crime rates at age 22 (peak crime age) using FBI data. The rates for those who grew up before leaded gas exposure were flat and rise in synch with leaded gas usage/exposure. She also points out that rates dropped the most in those states that had the greatest lead exposures.

and this report finds that that correlation is still there after factoring in the lead effect:"By the year 2020, when the effects of the Clean Air Act and Roev. Wade would be complete, violent crime could be as much as 70% lower than it would be if leadhad remained in gasoline, and as much as 35-45% lower than it would be if abortion had neverbeen legalized. At the same time, history suggests that other unknown factors would haveincreased crime by perhaps 3-5% per year."

My point exactly. The USA has always been way more into gasguzzling even in those days. So even if this reasearch is correct the effects are bound to be less pronounced elsewhere. At the same time this probably explains the crime levels in Mexico city...

Of course the more interesting correlation is a group that prides themselves on being enlightened and rational above all else, like the fans of the FSM would be so out of touch that they didn't know that there where still pirates on the high seas and that it is a real problem for shipping.

Of course the more interesting correlation is a group that prides themselves on being enlightened and rational above all else, like the fans of the FSM would be so out of touch that they didn't know that there where still pirates on the high seas and that it is a real problem for shipping.

It's actually just a problem with their survey method. They used to do a catch-release system to estimate the number of pirates, and identify them by markings on their earrings, patches, hooks, peglegs, etc. They also used a certain set of criteria (apart from the basic one of piracy) to identify pirates, and as the surveys have continued through the years they've failed to update their processes and criteria for changes in pirate fashions. (Basically, that pirates have come to favor other beverages apart from rum, the gradual improvements in prosthetics and the improvements in naval safety and changes in naval warfare which have reduced the incidence of dismemberment among pirates... the drastic changes in pirate lingo and their favored methods of doing business...)

As a result, the most recent surveys only turned up a very small number of pirates: Captain Hook (who hasn't aged for a considerable period of time), the Dread Pirate Roberts (whose centuries-long career defies all explanation - the survey teams are still trying to find an explanation), and a handful of others...

Of course, the disciples of the FSM have not overlooked these new facts. For a while, there has been a certain amount of doubt as to whether the results of this study really indicated that a decline in the number of pirates was the cause of global warming. Some said there could be other explanations, while others insisted that the whole situation merited further study and that it was too soon to draw any conclusions at all. Now, though, I think we can safely say, with a moderate level of cautious near-certainty, that the decline of piracy might not actually be entirely responsible for the increase in global temperature. There may be other factors, too.

Interesting - but couldn't this be a correlation != causation issue? Also it seems to imply that violent or criminal behavior is due to organic brain damage. Is that a given?

Correlation can be causation. Take smoking. Any "reasonable" person would suppose that smoking is bad for you. However, since you think it's bad, you can't test whether it is. The best you can do is look and see the correlation between smokers and lung cancer. No study has ever "proven" that smoking causes lung cancer. For all t

And on the flip side, the observed correlation could simply be a result of the improved socioeconomic climate of the past few decades, spurred on by the advent of video games, the improvement of people's income, and other stress-relievers.

Interesting - but couldn't this be a correlation != causation issue? Also it seems to imply that violent or criminal behavior is due to organic brain damage. Is that a given?

I think that correlation!=causation applies here.

I read a far more plausible reason in the book Freakonomics (great book btw), which postulates that the fall in crime rates in the US was attributable to the Roe v. Wade decision by the Supreme Court. The logic is that unwanted children are more likely to fall into a life of crime, due t

Interesting. If that were the case, then the impact should have been mostly restricted to states where abortion was illegal pre-Roe. (Sure, people do move, but it's a lot less likely that poor people are going to relocate to another state.) Is that seen?

Yes, actually, there were 5 states that legalized abortion in 1970, and those 5 states started a downward crime trend 3 years earlier than the rest of the states, where abortion was legalized in 1973.

"Lead has also been associated directly with delinquent, criminal, and aggressive behavior.
Denno [1990] finds that lead poisoning is the most significant predictor of disciplinary problems
and one of the most significant predictors of delinquency, adult criminality, and the number and
severity of offenses. Needleman et al. [1996] find a significant relationship between the amount
of lead in bone (a good measure of past exposure) and antisocial, delinquent, and aggressive
behaviors. Dietrich et al. [2001] followed a cohort of 195 inner-city youths from birth through
adolescence, and found a clear linear relationship between childhood blood lead levels and the
number of delinquent acts. In addition, Needleman et al [2002] showed that adjudicated
delinquents were four times as likely to have high lead levels than non-delinquents, and several
studies have shown that violent criminals exhibit higher levels of lead in their bodies than nonviolent
criminals or the general population.25"

It seems to me that this environmental hypothesis is testable (and confirmed) far beyond what is attainable for most theories in the social sciences.

You sound like you read the reports, and I am not prepared to start yet another huge project for myself by deciding to do in depth research, so I'll just ask...

Did any of these studies track the same individuals by economic class. I could definitely see a correlation between wealth and lead exposure, and could could also see there being an identical correlation between wealth and crime. If that is the case, it could very well mean that the connection isn't lead to crime, but wealth to crime.

It's one of at least two places lead was banned in the US in the last 40 years or so. Lead paint was once quite common as well. Lead solder used to be used in places where lead-free solder is now. So if the lead from gas turns out not to account for the total, lead from other sources may still have something to do with it.Oh, and lead-induced brain damage has strong statistical ties already to impulsive behavior and hampered mental function, which decline in the use of slide rules and increases in CPU power

Sometimes I wish slashdot allowed you to post pics on the comments section. Then I can directly post that graph that shows a correlation between a decrease in the pirate population and an increase in global warming.

Levitt's book is cited in the first paragraph of the paper, which is very interesting, but rather hard to understand on a (very) brief reading. Essentially, she says that lead contributes 56% to the drop in crime, while the availability of abortions contributes 29%.

And, obviously, 14.6% of the drop is due to increased use of corp syrup, making people too fat and lazy to bother committing violent crime, and the last.4% is due to the reduction in Satanists since the scare in the 1980s. Woo! I can pretend I'm a scientist too!

Disclaimer: I seriously don't want to start a flamewar or anything, please keep it civil.The legalization of abortion also occurred in a similar time frame and also has been attributed to a large statistical decrease in violent crime. http://www.accessmylibrary.com/coms2/summary_0286-10490717_ITM [accessmylibrary.com]

Are both studies wrong? One study? More bending of statistics to make up for science? Anyone specifically in the know?

In the end, anything that lowers the amount of kids in the street that have health and mental problems and/or are not wanted and/or are bored (thats a big one) and/or have crappy parents, will reduce crime significantly. So I'm guessing all these things are simply indirect.

Scientific research is being abused even more in this sensationalist age. Listen, experimental design is simple, really, and therein lies the problem. It's easy enough to come up with a study, run on a limited population, at a level of probability just under then better-than-random threshold that will prove your pet theory. The number of factors involved in the commission of crimes (violent or otherwise) are so diverse, that to attribute it to one factor is absurd. Could it be an increase in law enforcement

There are techniques to take some account of these factors. According to the NYT article, the study's author "uses small variations in the lead content of gasoline from state to state to strengthen her argument." So we have: 1) a correlation between violent crime and presence of lead in the environment, 2) support from state-by-state comparisons, 3) lead poisoning is linked to brain damage resulting in violent behaviors. Is that enough? Probably not - but it's suggestive, and with such sensational claims I expect there will be plenty of peer review.

You're also accusing the result of being a "pet theory". It may be. It may be that many or most scientists cheat. But we shouldn't assume - with no evidence whatsoever - that any particular scientist is acting in bad faith. Do that, and we'll find scientists living down to our expectations.

You may find the study "hard to believe", that it could "prove anything you like". If you don't examine the method, your complaint could also be leveled at any study you like. If you want better science, make specific criticisms - unless of course you don't want science at all.

Here's a crazy thought. You know what all of these trends have in common? They are tied to a general increase in liberal thought in America. Allowing abortions (personal freedom), forbidding lead additives (corporate regulation). So maybe it's other liberal policies that have helped with the decrease in violent crime.

Given the sheer number of variables and lack of evidence here other than some statistics with little to no hard data to back them up, it's all a crapshoot. You could as easily credit the Christian Church or the rise of paganism for the same result.

We offer evidence that legalized abortion has contributed significantly to
recent crime reductions. Crime began to fall roughly 18 years after abortion
legalization. The 5 states that allowed abortion in 1970 experienced declines
earlier than the rest of the nation, which legalized in 1973 with Roe v. Wade.
States with high abortion rates in the 1970s and 1980s experienced greater crime
reductions in the 1990s. In high abortion states, only arrests of those born after
abortion legalization fall relative to low abortion states. Legalized abortion
appears to account for as much as 50 percent of the recent drop in crime.

I saw those researchers talking about that on the Daily show once (or someone who wrote a book about it). No doubt, people will be more open to the lead paint idea than the abortion idea. Not because the data is any better or different but more so because religious beliefs are tied to abortion.

I'd like to know if forcing your beliefs on other people is worth twice as much crime? Is making cheaper, more effective paint worth twice as much crime? Personally I'd say no to both of those but I'm sure half the country disagrees with me on the first point.

I'd like to know if forcing your beliefs on other people is worth twice as much crime?

Pro-lifers believe that abortion is murder, and therefore a crime, so the answer in this case would be yes. There are alternatives to abortion, so your premise may be a false dilemma. How many offenders come from single parent homes? Foster homes? Adoptive two-parent homes?

> Instead of really helping people, we as a society have just chosen to get rid of them before they become problems.

That was the original point. Don't believe me, go read the writings of Ms. Sanger, the founder of Planned Parenthood. She was pretty open about her notions of Eugenics and eliminating the unfit and the 'inferior breeds' from the genepool. Amazing that Jesse Jackson and AL Sharpton never have any problems with supporting politicians who support Planned Parenthood and abortion since such a high percentage of the aborted are 'their'[1] people and that this WAS (even if they won't say it in public anymore) the stated purpose behind the founding of the organization.

[1] According to both the 'Reverends' and the MSM they are the Official spokesmen for all people of African descent in the US, whether the actual people want them as their leaders or not.

... the crime wave will recede from Eastern US cities like Baltimore, where every single property in the entire city was painted with lead [wikipedia.org] right up until the ban in 1978. Thing is, lead paint was used because of its durability, so there is no guarantee that these cities are even in the downward part of the curve yet, as the paint may just now be starting to chip and find its way into children's lungs/guts.

How about decreases in crimes by people who were never born, because their parents could get a legal abortion? And other family planning that made more kids who'd become old enough to commit crimes instead the product of more educated, well adjusted families? Also prenatal care and other health in ghettos.

The Civil Rights Revolution of the 1960s made a generation that came of age in the late 1970s through 1990s (and still coming today) a lot more well adjusted.

I question the timing. Giuliani is taking credit for the drop in crime in NY during his tenure as mayor (personally I think it was mostly Bratton - the police Commissioner). Guiliani is the leading GOP candidate for President '08. So, the NY Times and publishes a "study" that the drop in crime in the US was due to phasing out lead in gas. How convenient, expect more of this stuff as the '08 campaign heats up.

The book Freakanomics makes a good case for crime reduction based on the Roe v Wade - the legalization abortions. The logic goes that majority of kids who are not aborted end up being much more suspetible to crime. Another reason for reduced crime is increased police presence.

The drop in crime is actually due to LEGOS; the wonderful mental stimulating plastic brick toys which were launched in their plastic form in 1963. Yes, that is 10 yrs before the noted 1973 statistical start time. However, it took approx. 10 yrs for said toy to fully populate the American market.Thus, the statistical analysis clearly proves that LEGOS are directly responsible for the current drop in crime.

And why would this be? Because LEGO itself is derived from the term "Play Well". The millions of kids t

Reading the article, they already control for abortion, the average crime rate per year, the average crime rate for individual states, and even the effects of people moving from one state to another. The lead level measurements were finer grained than "lead existed before this date, then, everyone stopped using it"- they included state-by-state, year-by-year measurements in their lead data, adjusting for population density (as a surrogate for traffic density).

This was a sophisticated analysis; I wouldn't call it, as some commenters above have, "junk science". It would be surprising for their observed relation to hold, but their interpretation be incorrect. It would be interesting for someone to really come up with an alternative explanation of this paper's observations.

As a side note, I'm pretty sure that by now most lay people, and everyone reading this forum, is aware that correlation does not imply causation. And I'd be willing to guess that the vast majority of scientists have been aware of this elementary statistical fact for some time. It's likely that scientists take many potential influences into account before submitting for publication. So can we please exercise some restraint in the future and actually read the article before denouncing it as "junk science" because, as everyone knows, correlation is not causation? I am emphatically not asking people to take what the researcher says on faith, but if you decry the article without reading it, then your words are essentially noise.

Well now there's a theory that can be disproven if crime does not decrease in coutries with later date lead regulation. It sounds a bit farfetched as stated in the summary, but I can imagine lead as one of many many factors that cause a person to become likely to commit a crime.

Correlation does not imply causation. While the correlation may be very strong, causation cannot be assumed without ruling out many other potential contributing factors.

How many people have to post this needless gibberish over and over again? Is it some sort of karma whoring?

I mean, the effing SUMMARY got it 100% right:

"Even low levels of lead can cause brain damage, increasing the likelihood of behavioral and cognitive traits such as impulsivity, aggressiveness, and low IQ that are strongly linked with criminal behavior."

We know lead causes brain damage, and we know brain damage can lead to agressiveness, violence, etc.

"The NYTimes has a story on how the phasing out of leaded gasoline starting with the Clean Air Act in 1973 may have led to a 56% drop in violent crime in the US in the 1990s."

Key words: MAY HAVE LED TO. Its a hypothesis. Good.

They aren't asserting causation. They are noting a correlation, and using reasoning to form a hypothesis. So far so good.

An economics professor at Amherst College, Jessica Wolpaw Reyes, discovered the connection and wrote a paper comparing the reduction of lead from gasoline between states (PDF) and the reduction of violent crime. She constructed a table linking crime rates in every state to childhood lead exposure in that state 20 or 30 years earlier.

If lead poisoning is a factor in the development of criminal behavior, then countries that didn't switch to unleaded fuel until the 1980s, like Britain and Australia, should soon see a dip in crime as the last lead-damaged children outgrow their most violent years."

A useful prediction? Can it be? Holy shit. Its the full on scientfic method in action. Observe World, Formulate Hypothesis, Test Hypothesis.

I grant that is not the best possible test of the hypothesis, because its not a closed experiment, and its not really repeatable, and a lot of unknowns can get in the way, but we take what we can get. Human-centric sciences like medicine and psychology, or sciences like astrophysics or evolution don't have the luxury of perfect experiments - we can't raise humans in isolated bubbles, nor send a selection of stars into identicale blackholes nor watch a million isolated generations of people --

All we can do in these cases is come up with hypotheses and models, make predictions based on those models to see if we can find examples / counter examples in the observable world.

Overall, its good science here. If the dip in crime occurs where they occur when they predict it, it obviously it won't prove or disprove the hypothesis but it will add significantly to the body of evidence that supports it. If it doesn't occur then we'll have to refine or discard the hypothesis. If ultimately the hypothesis is junk it'll eventually get tossed out. Science is full of wrong hypothesises, but they are the best we have at any given time... that's how it works.

So what exactly do you object to here? That you felt the need to drone about the difference between causation and correlation. It seems everybody involved already got that memo.

"It couldn't be related to the fact that we have more criminals than ever cooling their heels in prison?"

TFA says that _violent_ crime is down. If there are fewer violent offenders, then how does that explain why the prisons are overfilled? The prison population exploded because we're putting more _nonviolent_ offenders in jail.

The total number of marijuana arrests far exceeds the total number of arrests for all violent crimes combined, including murder, manslaughter, forcible rape, robbery and aggravated assault.

Since 1992, approximately six million Americans have been arrested on marijuana charges, a greater number than the entire populations of Alaska, Delaware, the District of Columbia, Montana, North Dakota, South Dakota, Vermont and Wyoming combined. Annual marijuana arrests have more than doubled in that time.

Ok. This is getting a liiiittle bit offtopic, but I've gotta put in my US$0.02.

I'm from northern California (Santa Cruz, specifically) and I grew up in Georgia, where some people are still waging the Civil War. The only thing that I take from the southern side of the Civil War arguments for/against secession is states' rights. According to the Constitution, those powers not explicitly given the Federal government are reserved for the States (silly me; I left my pocket Constitution at home so someone else w

No, no. I don't think it's "okay", and I don't think it's "okay" to put people in jail for smoking a harmless plant which brings joy and wonder. If I balance my support for legalization against my support for democracy, democracy wins handily. When I balance my support for universal rights against my support for democracy, it's much closer, but democracy still wins. I would ask myself, is it better to live in 1700s Mississippi as a free man, or in 1900s USSR as a communist subject? I'd go with the former. S

except that they found a much better correlation than any of these that they considered interesting. They didn't say "hey! no more lead in gasoline and crime went down. Yippeee!" as you're making it out to be. If you don't believe me, try to publish your CPU speed theory. Much of science boils down to the careful study of correlation.

If you want to bash their study, fine, but at least RTFP, not just the summary on slashdot.

However, in this case, there was a direct correlation of time as well. Everything you listed happened in all the studied areas around the same time - and were they related to violent crime, the drop in violent crime would happen around the same time in all of these locations, which it didn't.

* Slide Rule and CPUs: This would show a marked drop which could be mapped by time and income bracket (as these would be the two factors mandating uptake), and not geographic region by state.* Global warming: This would show a marked drop which could be mapped by latitude, proximity to large bodies of water, and time, as these would all be mitigating/exaggerating factors in the relevant changes.

Find correlations with these factors, and maybe one of your theories can be tested. (and actually, global warming might be a good one - too much heat means more agitated people at lower latitudes, more happy people at higher latitudes, if we take the theory that crime to be inversely proportionate to happiness).

Occams razor people - this correlation works because it is one of the simpler explanations that fits what happened. Additionally, a testable prediction has been made from it - in 10-15 years, the theory will be tested.

These statistical correlations are a complete crock. There are a million things that have changed over the last few years that could also be attributed.Personally, I think the most likely cause is one of:

* Reduction in the use of slide rules. With calculators it's easier to get a job as a clerk.

* Increase in CPU speed. Too much time playing games == less time being bad.

* Global warming. It's getting too hot to commit crime.

Strength of correlation matters and if you have multiple cases to draw from (each sta

These statistical correlations are a complete crock. There are a million things that have changed over the last few years that could also be attributed.

One that was done piecemeal (so regression analysis could be performed) and which produced a strong signal under such analysis: Allowing law-abiding citizens to carry concealed weapons for self-protection against criminals. This drastically lowers the overall violent crime and injury/death rates (even if you DO count any crooks shot in self-defense as a "victim").

Interestingly, while many thought it might produce a short bloodbath (until criminals got the message that some of their victims might be armed), that didn't happen. Instead the violent crime rate just dropped, as criminals moved to less-armed areas, switched from muggings, armed robberies, carjackings, "hot" (occupied-dwelling) burglaries, to things like burglarizing UNoccupied homes and stores, or just found legal work. Rapes dropped like a rock, too (though they went up somewhat in nearby areas that hadn't yet liberalized their own laws.)

Turns out the crooks weren't SO stupid that they couldn't see the writing on that wall. And even those who didn't get the message right away usually weren't dumb enough to keep attacking, rather than run away, when they found themselves looking at the wrong end of a pistol.

(When Florida changed to non-discretionary CCW (i.e. the license has to be granted if the applicant jumps through the correct hoops and doesn't have a criminal record), one gang switched to hitting tourist in rental cars, on the assumption they'd be unarmed - both by airport regs and lack of a permit. Florida fixed that by removing the requirement that rental cars have distinctive markings/licenses and by issuing concealed carry permits to tourists. B-) Interestingly, even during the peak of the rob-the-Florida-tourists boom a tourist had less chance of being robbed in Florida than in California.)

Body loads of lead were very high in the later periods - especially among the upper, decision-making, classes. To the point that lead was believed to have been the major cause of a lack of fertility among the upper classes and the decline of those families.

Turns out it wasn't the lead plumbing - where the lead pretty much stayed in the pipes. They had figured out that if you put a lead liner in wine bottles the wine stayed sweet as it aged, rather than turning sour. But that's not because it DOESN'T turn to vinegar - instead the vinegar (acetic acid) reacts with the lead to form lead acetate - which is so sweet it's also called "sugar of lead". And it's REALLY well absorbed by the body.

The Darwin Awards are for people that remove themselves from the gene pool in obviously stupid ways. Given that lead poisoning isn't exactly obvious without an understanding of modern chemistry[*], I would cut the Romans some slack here.

I can neither confirm nor deny that. But from what I do know, I say it's a very high probability that there at least is no lead added to new gasoline. When you add lead to gasoline, you are really adding tetraethylead (you can go to an automotive store and buy it). It does two important things 1) increases octane and 2) lubricates the fuel system. From what I know about cars, engines designed for unleaded gasoline are much different than leaded. Especially around the time of the switch over. For one, the compression of the engines is significantly different: Leaded gasoline engines were pushing 12:1 or 14:1 compression ratios, for unleaded, even today you don't see much above 9:1. So that means, at least there isn't enough lead in today's gasoline to increase the octane enough to have a high compression engine. Likewise, the valve seats and such are much different in unleaded engines because of the lack of lubricity in the fuel (and hence exhaust) now.
I'd feel pretty confident saying that the amount of lean in fuel, if any, is orders of magnitude less than in leaded gasoline, and is negligible.

No one is saying that they person isn't responsible.I would rate this science as 'good', not great, or perfect, but certianly needing a closer look.The effects of lead on people is pretty well know. Based on other studies I have read, I believe it is not implausible that those effect would lead to more violent behavior.

An awful lot of "science" these days seems to forget about the last two items - and they're the most important.

Will the prediction turn out to be true? Who knows.... but that's the whole point. That's what makes this real science - somebody sticking his neck out in public, opening himself to the possibility of being wrong.